The purpose of this project is to use the mouse Beta-globin system as a model for eventual gene therapy of Beta-thaslassemia in humans. Recombinant DNA technology has been applied to study two areas important for proper regulation of a gene introduced into cells: a) the effect of DNA enhancing sequences on the mouse Beta-globin promoter, both in tissue cultured cells and in mice; and b) site specific integration of cloned genes. Various plasmids, called expression vectors, have been constructed to test the effect of known enhancers and to look for new enhancers. Attempts to isolate cellular factors which influence enhancer activity are also underway. Site specific integration of a cloned ribosomal DNA gene has been studied in cultural mouse cells where there are 300-350 copies of a homologous ribosomal gene.